Melissa Block interviews John Armbruster, a seismologist with Lamont-Doherty Earth Observatory, part of Columbia University, about why he believes the waste from fracking in Ohio has led to the earthquakes there. He says the injection of waste water from the fracking process created pressure on nearby faults, and he expects the quakes to continue — even after the process is stopped.

MELISSA BLOCK, HOST:

A series of earthquakes that have shaken Ohio over the last year were most likely caused by the injection deep underground of wastewater generated by drilling. That's the conclusion of a seismologist who's been studying the quakes and their connection to deep-injection disposal wells. Those wells in Ohio hold the waste fluids from hydraulic fracturing or fracking. Sand and chemicals are injected deep into the ground to fracture it, to make extracting natural gas easier. And then, something has to be done with that leftover wastewater, which brings us to John Armbruster, the seismologist, who Ohio regulators brought in to monitor these earthquakes. He's with Columbia University's Lamont-Doherty Earth Observatory.

JOHN ARMBRUSTER: This fracking fluid that you bring back is a waste that goes on a truck and is taken to a well, such as we are going to discuss, in Youngstown, Ohio, where this is disposed of by pumping it back into the ground again.

BLOCK: And we should be clear that there are separate concerns about the fracking process itself, which has to do with contamination of drinking water. We're talking about the aftermath, which is the waste fluid and what you have found, apparently, is that it is tied to this string of earthquakes in Ohio.

How did you come to that conclusion?

ARMBRUSTER: Well, we look at the evidence. Youngstown is an area which doesn't have a history of earthquakes. This disposal well started operating in December of 2010. Three months later, the earthquakes began and the earthquakes are trickling along. From March to November, you have nine earthquakes, all of a similar size, 2.5, 2.1, 2.7.

On Christmas Eve, there was a magnitude 2.7 earthquake. Our location of that Christmas Eve earthquake was about one kilometer from the bottom of the well and the location of the earthquake was sufficient evidence that there could be a link.

BLOCK: Help us understand, Mr. Armbruster, what would be going on seismically. If you have this waste water fluid deep underground, why would that trigger earthquakes?

ARMBRUSTER: I would compare it to a hydraulic jack. You're pumping this fluid into a crack and the pressure of this fluid is pushing against the two sides, encouraging the fault to slip.

BLOCK: The injection well near Youngstown, Ohio, that we've been talking about was actually shut down last week by the Department of Natural Resources in Ohio. There was then a magnitude 4.0 quake on Saturday after that. What would account for that and what does that say about what might happen going forward?

ARMBRUSTER: Well, the well has been pumping for a year. It's going to take a period of time comparable to that for the effects of this pumping to completely dissipate away.

BLOCK: Who is responsible for monitoring or regulating these wells?

ARMBRUSTER: Each state has an environmental protection agency or something with that type of name that licenses and regulates these wells.

BLOCK: Now, Ohio has something like 177 of these deep injection wells. I read a statement from an industry group which says that these kinds of wells have been used safely and reliably since the 1930s to dispose of waste water from drilling. Is the record pretty good, pretty safe, do you think?

ARMBRUSTER: Yeah. I don't argue with that. It's a matter of luck. When you have a well, is there an earthquake waiting to happen close enough to that well that you can trigger it to occur? I would advocate monitoring of wells to know when triggering of earthquakes first begins. Then you can decide whether to continue using that well.

BLOCK: Well, Mr. Armbruster, thanks for talking to us.

ARMBRUSTER: You're welcome.

BLOCK: John Armbruster is a seismologist with Columbia University's Lamont-Doherty Earth Observatory.

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